The Knee

The Knee

• Two Joints:

–Tibiofemoral

–Patellofemoral

Normal alingment due to difference between femoral condyles

The medial condyleextends further distally

Oatis, 2004

Osteochondral Defects

• Fractures of articular cartilage and underlying bone

• Shear and compressive forces

TibioFemoral AlignmentWhat are the

consequences of faulty alignment?

Triplanar Knee Motion

• A simple hinge joint would simply flex and extend

• This is not a simple hinge joint!!

Tibia on a fixed Femur

• FLEXION

– Backward Rolling

– Internal Rotation

– Varus

– Posterior Translation

• EXTENSION

– Forward Rolling

– External Rotation

– Valgus

– Anterior Translation

Femur on a fixed Tibia

• FLEXION

– Backward Rolling

– External Rotation

– Varus

– Anterior Translation

• EXTENSION

– Forward Rolling

– Internal Rotation

– Valgus

– Posterior Translation

Knee Motion

• Bony Geometry

• Soft Tissue Constraints

• Muscle Forces

Bony Factors

• Different size of the medial and lateral femoral condyles

• Different size of the articular surfaces of the femoral condyles and the tibialcondyles

• Variation in curvature from anterior to posterior

Medial Condyle is larger than the Lateral Condyle

Larger Femoral Condyles

What’s the consequence

of larger femoral

condyles?

Convex-Concave Rule

The Menisci

The Menisci

• Tibiofemoral load transmission• Shock absorption• Lubrication• Prevent synovial impingement• Distribute synovial fluid• Contribute to joint stability• Assist in gliding motion

My Third Law

Lev

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ean

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001

Movements of menisci• during flexion -

move posteriorly

• during extension -move anteriorly

…… the menisci follow, or stay with the, femoral condylesthe menisci follow, or stay with the, femoral condyles

extended flexing… menisci moveposteriorly unequally

R

Movements of menisci

• during lateral rotation of the tibia – the menisci follow the femoral condyles, e.g.

they remain with the femoral condyles while the tibia rotates

• during medial rotation (compare to lateral rotation)

Lateral rot. Medial rot.Neutral

R

…… the menisci follow, or stay with the, femoral condylesthe menisci follow, or stay with the, femoral condyles

The menisci attach to the tibia, but move with the femur.

What are the consequences?

LongitudinalHorizontal

Oblique Radial

Whiting and Zernicke, 1998

Let’s Review…

• Different sizes of femoral condyles means triplanar motion.

• Different sizes of the femoral and tibialcondyles means that gliding must accompany rolling.

• The meniscal reaction force is partially responsible for this gliding.

Anterior Cruciate Ligament

• Prevents anterior translation of the tibia with respect to the femur

• Or…• Stabilize in other

directions as well

Posterior Cruciate Ligament

• Prevents posterior translation of the tibia with respect to the femur

• Or…• Provides stability in

other directions as well

The Cruciates & Knee Motion

ACL assists in anteriorglide during flexion

PCL assists in posteriorglide during extension

Tibial:

•Anterior Translation

•Internal Rotation

•Valgus or Varus

PCL injuries…direct impact

Let’s Review…

• Larger medial condyle produces triplanarmotion

• Larger femoral condyles require a combination of rolling and gliding

• The menisci and cruciates are largely responsible for these gliding motions

Medial Collateral Ligament

• Restrains valgusloading

• Checks lateral tibial rotation

• Back-up anterior displacement

Lateral Collateral Ligament

• Resists varusstress

• Also limits lateral rotation

Why do we have a patella?

Patellar Motions

The Effect of the Quads on the Patella

Patellofemoral Pain

Force

AreaStress =

Trochlear Depth – 60° Flexion

Trochlear Depth – Full Extension

The knee is part of a kinetic chain.

Don’t look at it in isolation!

It’s not my fault!!

Heh! Heh!

Heh! Heh!